After soldering or adhering a chip to a metal substrate, the cooling of the soldered or adhered chip may result in very high thermo-mechanical stresses. This is due to the difference in the Coefficient of Thermal Expansion (CTE) between used materials, for instance, silicon and copper. Soldering is typically carried out at a temperature of about 380° C. while adhering is typically carried out at a temperature of about 200° C. The CTE of silicon is 2.5×10−6/° C. while the CTE of copper is 16.5/° C. During cooling from a high temperature to a low temperature, different materials contract differently due to different CTEs. The difference in contraction may lead to high thermo-mechanical stresses.
The high thermo-mechanical stresses may cause fractures within the substrates or cause thin chips (typically <<100 μm) to break. The substrate may also bend or warp due to the thermo-mechanical stresses. As a result, later manufacturing processes such as laser drilling, lamination and wire bonding may no longer be possible to be carried out. As such, the thermo-mechanical stresses due to the difference in CTE between different materials affects reliability of the chips.